PATHOPHYSIOLOGY
ORN was first described by Marx in 1983 as hypovascularity, hypocellularity, and local tissue hypoxia.[2, 3] Prior to this, many other theories existed regarding the etiology of ORN. The report by Marx, clinical experience, and subsequent research support this now widely accepted theory.

The irradiated mandible, periosteum, and overlying soft tissue undergo hyperemia, inflammation, and endarteritis. These conditions ultimately lead to thrombosis, cellular death, progressive hypovascularity, and fibrosis. The radiated bed is hypocellular and devoid of fibroblasts, osteoblasts, and undifferentiated osteocompetent cells.

Mandibular ORN develops most commonly after local trauma, such as dental extractions, biopsies, related cancer surgery, and periodontal procedures, but it may also occur spontaneously